Lithium ion secondary batteries are used in many electrically operated devices, more particularly, for use in daily life, in order to ensure energy supply. In the last few years, lithium ion secondary batteries have to an ever greater extent displaced secondary batteries used hitherto, particularly in the sector of portable electronic devices. The reason for this is that lithium ion secondary batteries can have a high energy density.
For negative electrodes of lithium ion secondary batteries, principally carbon is used as the host material. The carbon may be in the form, for example, of what is called conductive black or in the form of (likewise conductive) graphite. Carbon in the form of conductive black or graphite is particularly notable in that, and is used because, carbon has only very small changes in volume in the course of reversible intercalation of lithium in charging and discharging operations. However, an important disadvantage of the use of carbon is that a maximum capacity of, for example, graphite is limited to about 372 mAh/g.
In view of the restrictions resulting from carbon, i.e., conductive black or graphite, there are efforts to find alternative materials, or to optimize known ones, for negative electrodes of lithium ion secondary batteries. In this regard, WO 2005/096414 A2 proposes using nanoscale silicon particles as well as a customary binder. Silicon can bind lithium to a high degree, which results in a high theoretical specific capacity. However, silicon, on reversible uptake of lithium, is subject to a significant change in volume, which is disadvantageous. WO 2005/096414 A2 therefore proposes using nanoscale silicon particles for production of a material for a negative electrode. This is supposed to ensure sufficient stability of the electrode material on reversible incorporation and discharge of lithium with small irreversible losses of capacity. However, studies have shown that cycling stability is achieved only at low current stresses on the electrode. In the case of constant current cycling operations with high current stresses, a significant decline in capacity occurs after a few cycles.
Also known is use of alloys of silicon as an electroactive material in negative electrodes for lithium ion secondary batteries, for example, from U.S. Patent Publication No. 2009/0061322 A1. In this case, silicon-titanium alloys or else alloys of silicon with copper or other silicon alloys may be used. In addition, the silicon in these alloys has been doped, for example, with boron, aluminum or gallium. One disadvantage of these materials is the complex production or the requirement for doping of the material.
Moreover, in accordance with U.S. Pat. No. 6,300,013 B1, silicon is used as an electroactive material in negative electrodes for lithium ion secondary batteries. In this case, silicon is in the form of silicon alloys, especially alloys in the silicon-magnesium alloy system. These alloys, however, are probably also subject to a relatively great change in volume on reversible incorporation and discharge of lithium, and therefore a high carbon content of more than 50 percent by weight (% by weight) is necessarily provided at the same time in order to buffer any change in volume.